In recent years, media-content reproducing apparatuses involving digital processing have been providing various functions due to technological advancement and increasing availability of various digital media-content reproducing apparatuses such as digital television systems and optical disk devices. As functions within such a background, for example, functions are more often provided than ever in such apparatuses to mix main audio of digital television broadcast or disk-content-reproduced audio with external audio such as guidance audio or an alert sound, and to output the mixed audio. Furthermore, if such a mixing process of external audio is implemented in a same apparatus, especially in a semiconductor device such as a system LSI, there is an increasing demand to implement these processes all at once, from decoding and reproduction processes of bit streams, through acoustic processing of reproduced sound, to a mixing process with external audio, in order to minimize the cost drivers in relation to functionality expansion.
A sound reproducing device for meeting such a demand is achieved by, for example, a configuration as shown in FIG. 41.
A sound reproducing device 7000 shown in FIG. 41 includes a control section 1100, a decoder section 1200, a sampling-frequency conversion section 1300, an acoustic processing section 1400, and an additional-audio addition section 1500. The additional-audio addition section 1500 includes therein an additional-audio generation section 1510 and an adder 1520.
Functions provided in the acoustic processing section 1400 include, for example, a sound-quality enhancement process involving an oversampling process, a sound-quality adjustment function for setting speakers, a channel expansion process, sound-volume processing, etc.; the acoustic processing section 1400 is instructed to perform these processes through the control section 1100 from the outside world.
A reproduction process by the sound reproducing device 7000 is performed according to the flowchart shown in FIGS. 42-43.
First, the decoder section 1200 decodes an audio bit stream input from the outside world, generates a decoded PCM signal (ST701 and ST702), and then outputs decoding information to the control section 1100, including decoder type information, sampling frequency information, channel configuration information, etc. (ST703), which are obtained when decoding the audio bit stream.
The control section 1100 receives reproduction-instruction information from the outside world and the decoding information from the decoder section 1200 (ST705), and determines whether or not to perform sampling frequency conversion and whether or not to perform various acoustic processing on the decoded PCM signal (ST706 and ST707). For example, the reproduction-instruction information received from the outside world includes instructions on acoustic processing including, among others, a sound-quality enhancement process involving an oversampling process provided in the acoustic processing section 1400. Here, a case where an instruction on a sound-quality enhancement process involving an oversampling process is provided will be described as an example. In this case, since the reproduction-instruction information received from the outside world includes an instruction on a sound-quality enhancement process involving an oversampling process, the sampling frequency of the output PCM signal output from the sound reproducing device 7000 is different from the sampling frequency of the decoded PCM signal, but is equal to a sampling frequency after the oversampling process. For example, if the decoded PCM signal is at 48 kHz, and the sampling frequency for the sound-quality enhancement process is 96 kHz, then the sampling frequency of the output PCM signal is 96 kHz.
In such a case, since the control section 1100 determines that sampling frequency conversion should be performed (No at ST707), the control section 1100 instructs the sampling-frequency conversion section 1300 on an oversampling process of the decoded PCM signal (ST708), and the sampling-frequency conversion section 1300 performs an oversampling process according to the instruction of the control section 1100 (ST709).
Next, the acoustic processing section 1400 receives the reproduction-instruction information from the control section 1100 (ST710), and performs the acoustic processing on the decoded PCM signal according to the instruction (ST711). Since the reproduction-instruction information here includes a sound-quality enhancement process, the acoustic processing includes the sound-quality enhancement process.
Then, the control section 1100 transmits the sampling frequency information on the output PCM signal to the additional-audio addition section 1500, and instructs the additional-audio addition section 1500 to generate an additional-audio PCM signal, and to add the additional-audio PCM signal with the decoded PCM signal after the acoustic processing (ST712).
The additional-audio addition section 1500 first receives the additional audio data form the outside world (ST713), and generates the additional-audio PCM signal in the additional-audio generation section 1510 therein (ST714). Since, at this stage, the sampling frequency of the additional-audio PCM signal needs to be the same as that of the decoded PCM signal after the acoustic processing, the process of generating the additional-audio PCM signal includes an oversampling process to convert the sampling frequency to 96 kHz. In addition, the additional-audio PCM signal generated in the additional-audio generation section 1510 and the decoded PCM signal on which the acoustic processing has been performed in the acoustic processing section 1400 are added together by the adder 1520 (ST715), and the result is output to the outside world as the output PCM signal (ST716).
Performing the processes described above achieves the mixing process of the decoded PCM signal obtained from an audio bit stream and the additional audio data input from the outside world.
Note that Patent Document 1 describes one of the technologies similar to this conventional example. Patent Document 1 relates to a process to mix a plurality of digital audio data different from each other in sampling frequencies, and the object is to achieve a mixing process throughout in the form of digital signals.